Crosslinked vinyl halide polymers as flame retardant additives for thermoplastics

ABSTRACT

THERE ARE DISCLOSED FIRE RETARDANT POLYBLENDS COMPRISING THERMOPLASTIC POLYMERS INTIMATELY ADMIXED WITH A CROSSLINKED COPOLYMER OF A VINYL HALIDE, PREFERABLY A CROSSLINKED VINYL CHLORIDE COPOLYMER. THESE FIRE RETARDANT POLYBLENDS MAY BE UTILIZED IN A VARIETY OF COATING, IMPREGNATING AND ESPECIALLY MOLDING APPLICATIONS WHEREIN IT IS DESIRED TO PROVIDE FIRE RETARDANCY TO THE RESULTING END PRODUCT.

United States Patent 3,780,141 CROSSLINKED VINYL HALIDE POLYMERS AS FLAME RETARDANT ADDITIVES FOR THERMOPLASTICS Jung Il .Iiu, Irvington, and Paul Kraft, Spring Valley, N.Y., assignors to Stauifer Chemical Company, New York,'N.Y. No Drawing. Filed Jan. 21, 1971, Ser. No. 108,632 Int. Cl. C08f 29/22, 29/24 US. Cl. 260-897 C 15 Claims ABSTRACT OF THE DISCLOSURE There are disclosed fire retardant polyblends comprising thermoplastic polymers intimately admixed with a crosslinked copolymer of a vinyl halide, preferably a crosslinked vinyl chloride copolymer. These fire retardant polyblends may be utilized in a variety of coating, impregnating and especially molding applications wherein it is desired to provide [fire retardancy to the resulting end product.

BACKGROUND OF THE INVENTION As is known to those skilled in the art, the so-called' burning thermoplastics which include, for example, polystyrene, the polyolefins, polymethyl methacrylate and the ABS resins, all possess the undesirable property, upon being ignited, of continuing to burn until substantially consumed. Accordingly, these hard and, in many instances, optically clear materials which are widely em.- ployed for the preparation of a broad range of consumer and industrial articles cannot, ordinarily, be used in many applications involving their use in building interiors or in products which will be subjected to prolonged exposure to high temperatures. Thus, the burning thermoplastics fail to display fire or flame retardant properties which would, otherwise, permit them to either meet the standards set by various building codes or to be safely employed in place of more costly materials.

Prior attempts to provide fire retardant compostitions from these burning thermoplastics have involved their blending with avariety of extraneous additives such, for examples as antimony oxides, halogenated parafiins, halogenated hydrocarbons and low molecular weight phosphate esters. Many of these additives, such as antimony trioxide, are quite expensive while, in general, their efiFective utilization requires their presence in rather high concentrations which adversely efiect the physical properties of the treated polymers. Thus, the inherent hardness and, in some instances, the clarity of the thermoplastic polymers are particularly prone to deterioration in the presence of the high concentrations of these additives which are necessary in order to achieve a self-extinguishing polymer composition.

It is, therefore, the prime object of this invention to provide novel fire retardancy additives which can be used, per se, as fire retardant materials or which can, preferably, be admixed with burning thermoplastics so as to yield polyblends characterized by their excellent fire retardant properties which are achieved without any serious diminution of the physical properties of such blends. Various other objects and advantages of this invention will be apparent from the disclosure thereo ich follows hereinafter.

TECHNICAL DISCLOSURE OF T E INVEN ON It has now been found that crossli ed copolymeixof the vinyl halides, particularly of vin l chloride, can be blended with burning thermoplastics so as to yield e retardant polyblends which are devoid of any detriment 1 effects upon their physical properti s. Moreover, it s See truly surprising and advantageous to find that the polyblends resulting from the process of this invention display an outstanding degree of compatibility with various burning thermoplastics. Thus, it is well known to those skilled in the art that physical blends of two or more polymers are generally characterized by their inherently poor mixing.

It should be noted, at this point, that the use of the term crosslinked in describing the novel fire retardant copolymers of this invention will indicate to those skilled in the art that they possess a highly intermeshed, threedimensional configuration or network rather than a simple linear or branched structure of the type found in noncrosslinked copolymers. Thus, such crosslinked polymers may be further characterized by the fact that they will not lose more than about 20% of their total weight upon being extracted with methanol in a Soxhlet extractor. In addition, the use in this disclosure of the term copolymer is meant to denote a polymer derived from two, three or more distinct monomer species.

The novel fire retardant additives of this invention are thus seen to comprise crosslinked copolymers of:

(1) One or more vinyl halides selected from the group consisting of vinyl chloride, vinyl bromide and vinyl fluoride with the use of vinyl chloride being preferred because of its lower cost and more wide spread commercial availability; and,

(2) One or more polyfunctional ethylenically unsaturated monomers, i.e. one or more monomers containing two or more polymerizable, ethylenically unsaturated bonds including, for example, allyl methacrylate, divinyl benzene, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, diallyl adipate, 2-vinyl oxyethyl ether, methylene-bisacrylamide, diethylene glycol diacrylate, ethylene glycol diacrylate, divinyl ether, diallyl fumarate, diallyl phthalate, divinyl sulfone, divinyl carbitol, butylene dimethacrylate, trimethylene glycol diacrylate, butylene glycol diacrylate, pentamethylene glycol diacrylate, glyceryl triacrylate, octylene glycol diacrylate, trimethylene propane triacrylate, the tetraacrylate ester of pentaerythritol and the diallyl phosphonates such as ethyl diallylphosphonate. Optimum results are, however, obtained by the use of allyl methacrylate since its use leads to a higher degree of conversion of the vinyl chloride monomer to the form of polymeric moieties as Well as a more extensive degree of crosslinking as indicated by the presence of little, if any, methanol extractable residues in the resulting crosslinked copolymer.

The crosslinked copolymeric fire retardant additives of this invention may also, if desired, contain one or more optional monovinyl, i.e. monoethylenically unsaturated, comonomers. These optional comonomers can include: vinylidene halides such as vinylidene chloride, vinylidene bromide and vinylidene fluoride; alphaolefins such as ethylene, propylene and butylene; vinyl esters of carboxylic acids such as vinyl acetate, vinyl butyrate, and vinyl stearate; the C C alkyl esters of acrylic and methacrylic acid such as methyl methacrylate, bromomethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, Z-ethylhexyl acrylate and lauryl acrylate; aryl, haloand nitro-substituted benzyl esters of acrylic and methacrylic acid such as benzyl acrylate and 2-chlorobenzyl acrylate; ethylenically unsaturated monocarboxylic acids such as acrylic and methacrylic acids; ethylenically unsaturated dicarboxylic acids, their anhydrides and their C C monoand dialkyl esters such as aconitic acid, fumaric acid, maleic acid, itaconic acid, citraconic acids, maleic anhydride, dibutyl fumarate and monoethyl maleate; amides of ethylenically unsaturated carboxylic acids such as acrylamide and methacrylamide; vinyl pyrrolidones such as N-vinyl-Z-pyrrolidone; vinyl aryl compounds such as styrene and alpha-methyl styrene; nitriles of ethylenically unsaturated carboxylic acids such as acrylonitrile, methacrylonitrile and u-chloroacrylonitrile; C C- alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and stearyl vinyl ether; and, vinyl and allyl phosphonates such as bis(beta-chloroethyl) vinylphosphonate and bis(beta-chloroethyl) allylphosphonate. Preferred for use as optional comonomers are the vinylidene halides, particularly vinylidene chloride, and the vinyl and ally phosphonates.

With respect to proportions, the crosslinked vinyl halide copolymers applicable for use as fire retardant additives for preparing polyblends with burning thermoplastics may contain from about 50 to 99 and preferably about 60 to 98%, by weight, of one or more of the above described vinyl halides; from about 1 to 50 and preferably about 2 to 40%, by weight, of one or more of the above described polyfunctional ethylenically unsaturated monomers; and, from to about 49%, by weight, of one or more of the above described optional monovinyl comonomers.

The above described copolymers may be prepared by means of any convenient, free radical initiated polymerization technique known to those skilled in the art including such procedure as suspension, emulsion and solution polymerization.

Thus, in preparing these crosslinked vinyl halide copolymers by means of a suspension polymerization technique, the reaction is conducted in an aqueous medium containing from about 0.01 to 10%, as based on the total weight of the monomer mixture, of a suspension agent such, for example as gelatin, starch, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose carboxymethyl cellulose, talc, clay, polyvinyl alcohol and the like. As a catalyst for the polymerization, one may use from about 0.01 to 5%, as based on the total weight of the monomer mixture, of a monomer soluble azo or per oxide catalyst such, for example, as azobisisobutyronitrile, lauroyl peroxide, benzoyl peroxide, isopropylperoxy dicarbonate, t-butyl peroxypivalate and the like.

Polymerization may ordinarily be initiated by heatnig the system to a temperature in the range of from about 45 to 100 C. for a period of from about 4 to 24'hours with agitation being applied throughout the course of the reaction. The resulting product will comprise an aqueous suspension of the desired copolymer which will be in the form of particulate solids having a resin solids content in the range of from about to by weight. These copolymer particles will have a particle size in the range of from about 10 to 500 microns with a range, of from about 10 to 50 microns being preferred when these copolymers are to be used as fire retardant additives for preparing polyblends with burning thermoplastics.

In preparing these copolymers by means of an emulsion polymerization procedure, the selected monomers are dispersed in an aqueous medium containing from about 0.01 to 10%, by weight of the monomers, of one or more anionic, non-ionic or cationic emulsifiers such, for example, as the alkyl carboxylic acid salts, the alkyl sulfate salts, the alkyl sulfonate salts, the alkyl phos phate salts, the alkyl sulfosuccinate salts, the alkyl aryl ether alcohols and the alkyl aryl polyether sulfate salts, The aqueous monomer emulsion is then heated for about 4 to 24 hours at a temperature of from about 25 to 100 C. in the presence of from about 0.01 to 5%, by weight of the monomer mixture, of a water soluble free radical initiating catalyst such, for example, ammonium, sodium or potassium persulfate, hydrogen peroxide or a redox system comprising a mixture of a persulfate with an alkali metal bisulfite, thiosulfate or hydrosulfite.

And, in preparing these copolymers by means of a solution polymerization procedure, the selected monomers are first dissolved in an organic solvent such, forexample, as benzene, toluene, cyclohexanone, acetone, tetrahydrofuran, trichloroethylene, dimethylformamide or dimethylsulfoxide. The resulting solution is then heated for from about 4 to 24 hours at a temperature of from about 30 to 100 C. in the presence of a monomer soluble azo or peroxide catalyst as exemplified by the compounds listed, hereinabove, in describing the suspension polymerization process.

Specific crosslinked vinyl halide copolymer composi tions which have been found to provide particularly good results as additives for the preparation of fire retardant, thermoplastic polymer compositions, i.e. polyblends, are a 95:5 vinyl chloridezallyl methacrylate copolymer, a 90:10 vinyl chloride:allyl methacrylate copolymer and a 90:10 vinyl bromidezallyl methacrylate copolymer.

In all cases, the novel crosslinked vinyl halide copolymer additives of this invention have been found to provide blends with thermoplastic polymers which are characterized by their outstanding fire retardancy, their ease of blending and their retention of physical properties such as hardness, tensile and impact strength. As used in this disclosure, the term fire retardant or flame retardant is intended to refer to that particular porperty of a material which provides it with a degree of resistance to ignition and burning. Thus, a fire or flame retardant composition is one which has a low level of flammability and flame spread.

The thermoplastic polymers which can be used in preparing polyblends with the novel crosslinked vinyl halide copolymers of this invention include:

(1) Polymers of vinyl chloride including polyvinyl chloride and the random and graft copolymers of vinyl chloride with a minor proportion of one or more of the above described group of vinyl comonomers which were listed as optional comonomers for use in preparing the crosslinked vinyl halide copolymers;

(2) Polymers of nitriles of ethylenically unsaturated acids including polymethacrylonitrile, polyacrylonitrile and the copolymers of methacrylonitrile or acrylonitrile with a minor proportion of one or more vinyl monomers such as the lower alkyl acrylates and methacrylates, styrene and alpha-methyl styrene;

(3) Polymers of methyl methacrylate including polymethyl methacrylate and the copolymers of methyl methacrylate with minor proportions of one or more alpha, beta-ethylenically unsaturated monomers which are polymerizable therewith including the C -C alkyl, cycloalkyl and bicycloalkyl esters of acrylic acid and the C -C alkyl, eycloalkyl and bicycloalkyl esters of methacrylic acid such, for example, as ethyl acrylate and methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, norbornyl acrylate, and cyclohexyl acrylate; vinyl aryl compounds such, for example, as alpha-methyl styrene and styrene; and, nitriles of alpha, beta-ethylenically unsaturated carboxylic acids such, for example, as acryloni trile and methacrylonitrile. From the above given group, the use of the C -C alkyl esters of acrylic acid, particularly ethyl acrylate, and of the C -C alkyl esters of methacrylic acid is preferred;

(4) Acrylonitrile-butadienestyrene resins, commonly referred to as ABS resins, which generally comprise either a mixture of a 60 to :40 to 20 styrene:acrylonitrile copolymer with from about 10 to 40%, by weight, of a 5 to 40:95 to 60 acrylonitrile-butadiene copolymer or a mixture of a 60 to 80:40 to 20 styrenezacrylonitrile copolymer with from about 10 to 40%, by weight, of a graft of the latter copolymer onto polybutadiene;

(5) Poly(alpha-olefins) such as polypropylene and polyethylene and copolymers of one or more alpha-olefins, such as ethylene or propylene, with a minor proportion of one or more ethylenically unsaturated monomers including 4-methyl pentene-l, butene-l, orbornene and its derivatives; cyclopentadiene; cyclopentene; cyclobutene; vinyl acetate; the C C alkyl acrylate and methacrylate esters; as well as blends of the homoand copolymers of alpha-olefins with other types of thermoplastic polymers;

(6) Polymers of styrene including polystyrene, poly- (alpha-methyl styrene) and poly(tertiary butyl styrene) and copolymers of styrene, alpha methyl styrene or tertiary butyl styrene with a minor proportion of one or more ethylenically unsaturated comonomers such, for example, as nitriles 0f ethylenically unsaturated carboxylic acids including acrylonitrile and methacrylonitrile; C -C alkyl esters of acrylic and methacrylic acids such, for example, as methyl methacrylate and Z-ethylhexyl acrylate; and, graft copolymers of styrene, tertiary butyl styrene or alpha-methyl styrene with polybutadiene and other hydrocarbon elastomers;

(7) Cellulosic resins including cellulose esters and mixed esters such, for example, as cellulose nitrate, cellulose acetate-butyrate, cellulose acetate-propionate and cellulose ethers such, for example, as ethyl cellulose;

(8) Polyamide resins, i.e. the resins made by the condensation of dior polyamines with dior polybasic acids or by polymerization of lactams or amino acids. Typical polyamides include nylon which is made from pyrrolidone; nylon 6 obtained by polycondensation of caprolactam; nylon 66 obtained by the condensation of hexamethylene diamine with adipic acid; nylon 610 obtained by the condensation of hexamethylenediamine with sebacic acid; nylon 7 which is a polymer of ethyl aminoheptanoate; nylon 9 made from 9-aminononanoic acid; and, nylon 11 made from ll-amino undecanoic acid; I

(9) Polyester resins, i.e. the resins produced by the condensation of saturated or unsaturated dibasic acids, such as terephthalic, maleic, fumaric, isophthalic, adipic and azelaic acids with dihydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol and dipropylene glycol. Where the resin is made with an unsaturated acid, a polymerizable monomer such, for example, as styrene, vinyl toluene, diallyl phthalate, methyl methacrylate; chlorostyrene, alpha-methyl styrene, divinyl benzene or triallyl cyanurate is often included in the composition;

(10) Polyurethane resins, i.e. the resins formed by the reaction between a bior polyfunctional hydroxyl containing compound, such as a polyether or polyester, and a dior polyisocyanate such as toluene diisocyanate or diphenylmethane-4,4'-diisocyanate;

(11) Polycarbonate resins, i.e. the resins derived from the reaction between a difunctional alcohol or phenol, such as bisphenol A, and phosgene or an alkyl or aryl carbonate;

(12) Polyacetal resins, i.e. the resins derived from the anionic polymerization of formaldehyde to obtain a linear (13) Polyphenylene oxide resins made by the oxidative polymerization of 2,6-dimethylphenol in the presence of a copperamine-complex catalyst;

(14) Polysulfone resins, i.e. the resins containing an S0 linkage as derived from the reaction of sulfur dioxide with olefins such as l-butene or, more preferably, by reaction of bis-phenol A with 4,4-dichlorodiphenyl sulfone.

(15) The acrylate:styrenezacrylonitrile resins, commonly referred to as ASA resins, which comprise copolymers containing a major proportion of a C -C alkyl acrylate ester elastomer upon which is grafted about 65- 95%, by weight of the latter copolymer, of a 7080:3020 styrene: acrylonitrile copolymer.

(16) The methacrylate:butadiene:styrene resins, commonly referred to as the MBS resins, which comprise a minor proportion of a methyl methacrylate:styrene:acrylonitrile terpolymer grafted and/or blended with either polybutadiene or a copolymer of butadiene and minor proportions of such comonomers as, for example, styrene and acrylonitrile.

In effect, one may utilize any thermoplastic polymer, i.e. any polymer that may be softened by heat and then regain its original properties on cooling, in preparing fire retardant polyblends with the novel crosslinked vinyl halide copolymer additives of this invention.

The actual blending of these crosslinked vinyl halide copolymer additives with the selected polymeric substrate,

i.e. with any one or more of the above described thermoplastic polymers, may be accomplished by means of any convenient procedure which will result in an intimate admixture of the additive within the mass of the substrate polymer. Thus, for example, an aqueous suspension containing the particles of the copolymer additive may simply be blended or otherwise admixed with the substrate polymer which should, preferably, be in the form of an aqueous latex or suspension. Or, if desired, the copolymer additive and the thermoplastic polymer substrate may be admixed while each is in the form of a solid powder.

The blending operation may also be carried out by means of a procedure in which the thermoplastic polymer which comprises the substrate is itself polymerized while in the presence of an aqueous emulsion or suspension or organic solvent solution containing one or more of the previously prepared crosslinked copolymer additives of this invention.

With respect to proportions, the amount of crosslinked vinyl halide copolymer which may be admixed with a thermoplastic polymer substrate will depend, primarily, upon such factors as the particular crosslinked vinyl halide copolymer and thermoplastic polymer substrate which are to be blended with one another, the degree of fire retardancy desired in the resulting blend, the degree of clarity, hardness and other specific physical properties which are sought as Well as other technical and economic considerations known and understood by those skilled in the art. However, in order to attain a composition which will be self-extinguishing, it is generally desirable to introduce an effective concentration of the copolymer additive which will be suflicient to provide the resulting blend with at least about 5%, by weight, of halogen, i.e., chlorine, bromine, or fluorine, derived from the crosslinked vinyl halide copolymer. Thus, depending upon the concentration of the vinyl halide in the croslinked copolymer, the polyblends containing the novel additives of this invention will contain from about 10 to 50%, by weight, of one or more of these crosslinked vinyl halide copolymers.

It is to be noted, at this point, that it is particularly surprising to find that polypropylene yields compatible polyblends with the crosslinked vinyl halide, and especially with the crosslinked vinyl chloride, copolymer additives of this invention. Thus, inasmuch as this commercially valuable polyolefin polymer cannot ordinarily be blended with conventional, i.e. uncrosslinked, polyvinyl chloride it would not, therefore, be expected that its polyblends with the additives of this invention could be easily admixed so as to yield highly compatible products in which the crosslinked copolymer additives exist in the form of distinct domains within the mass of the polypropylene substrate. Moreover, these polypropylene polyblends exhibit good fire retardancy characteristics without any significant heat degradation even at the elevated milling temperatures ordinarily employed for the milling of polypropylene.

The fire retardant polyblends of this invention can be prepared so as to contain various optional additives which may includue plasticizers such as the alkyl esters of phthalic, adipic and sebacic acids such, for example, as dioctyl phthalate and ditridecyl phthalate and aryl phosphate esters such, for example, as diphenyl 2-ethylhexyl and tricresyl phosphate, etc.; lubricants and mold release agents such as stearic acid or its metal salts, petroleum based waxes, mineral oils, polyethylene waxes, etc.; and heat and light stabilizers such as barium, cadmium, calcium or zinc soaps and phenates, basic lead compounds, organo-tin compounds such as dialkyl tin mercaptides and dialkyltin maleates, thiolauric anhydride and n-butyl stannoic acid, epoxidized oils, alkyl diphenyl phosphite, triaryl phosphites, phenyl salicylates, benzophenones and benzotriazoles, etc. For a more complete listing of plasticizers, lubricants, stabilizers and other functional additives, one may consult Polyvinyl Chloride by H. A. Sarvetnick published by Van Nostrand Reinhold Co., New York, N.Y., in 1969.

These polyblends may also contain fillers, pigments, dyes, opacifying agents, decorative additives such as reflective metal foils or flakes, and other imbedded solid objects such as fiber glass, textile fibers, asbestos, paper, and the like, provided that they do not detract from the flame retardancy of these products. In addition, the compositions may contain other flame retardants such as antimony compounds, chlorinated paraffius, perchlorinated alicyclic compounds, bromine containing organic compounds, halogenated alkyl phosphates or phospohnates, alkyl acid phosphates, or small concentrations of phosphoric acid. Thus, it may be noted, at this point, that the fire retardancy of the novel polyblends of this invention can be still further improved by the addition of concentrations of antimony trioxide which are substantially below those normally utilized when this costly additive is used by itself as a fire retardant additive for burning thermoplastics.

The novel polyblends of this invention, comprising blends of any of the above described thermoplastic polymers With one or more of the crosslinked vinyl halide copolymer additives of this invention, may be utilized in any of the coating, impregnating and especially in the molding applications known to those skilled in the art wherein it is desired to provide fire retardancy to the resulting end product. For example, these compositions may be used for preparing such diverse items as calendered films, blow molded bottles, extruded and blown films, extruded and shaped articles such as panels, tubes, sheets, rods, fibers and particularly with polypropylene and other polyolefin fibers, and in carrying out such processes as injection molding, fluidized bed coating, electrostatic powder spraying and rotational coating, etc. More particularly, those polyblends which are optionally clear such, for example, as those based upon homoor copolymers of methyl methacrylate or homoor copolymers of styrene may be utilized for preparing such articles as lenses, aircraft canopies, windows, Windshields, lighting fixtures and advertising displays. Applications wherein optical clarity is not essential include such automotive applications as seat backs, door panels, instrument panels, head rests, arm rests, package shelves, plated hardware, radiator grills, fender extensions and liners, wheel covers and gas tanks. Non-automotive applications include their use as structural and decorative components for both the interiors and exteriors of conventional houses and mobile homes and as structural and decorative elements of business machines and electrical appliances.

In addition to being used as fire retardant additives for the preparation of fire retardant polyblends with burning thermoplastics, the crosslinked vinyl halide copolymer additives of this invention may be used, per se, in any of the various coating, adhesive, laminating, impregnating and molding applications known to those skilled in the art. Thus, they may be coated upon and/or absorbed by all types of substrates to which it is desired to impart fire retardant properties. They may, therefore, be used as coatings, irnpregnants, fillers, laminants, and adhesives for such substrates as wood; paper; metals, textiles based on either natural or synthetic fibers or blends thereof; synthetic polymer films such as those based upon polyolefins, regenerated cellulose, i.e. cellophane, polyvinyl chloride, polyesters and the like; leather; natural and synthetic rubber; fiberboard; and synthetic plastics prepared by means of either addition or condensation polymerization techniques.

The following examples will further illustrate the embodiment of this invention. In these examples, all parts given are by Weight unless otherwise noted.

Example I This example illustrates the preparation of a crosslinked vinyl halide copolymer additive and its use in the preparation of a fire retardant polyblend with polypropylene.

Ninety parts of vinyl chloride and ten parts of allyl methacrylate are suspension polymerized in a solution of 0.5 part of methyl cellulose in 300 parts of deionized water which also contains 0.5 part of t-butyl peroxypivalate as an initiator. The latter mixture is stirred at 60 C. for 10 hours while in a nitrogen atmosphere. The resulting crosslinked 10 vinyl chloridezallyl methacryl ate copolymer is isolated by filtration followed by washing with water and drying at 70 C. for 24 hours. The copolymer is obtained in a yield of 98% and contains 50%, by weight, of chlorine.

A polyblend containing polypropylene along with 30%, by weight, of the above described crosslinked copolymer is prepared by milling a mixture of these two resins for 10 minutes on a two-roll mill in which the front roll is at a temperature of 185 C. and the back roll is at 130 C. As shown in the following table, the resulting blend, as compared with unmodified polypropylene, displays re duced flammability upon having its limiting oxygen index (LOI) determined by means of ASTM D-2863; the latter procedure also being described by Fenimore and Martin in the November 1966, issue of Modern Plastics. In brief, this procedure directly relates flame retardancy to a measurement of the minimum percentage concentration of oxygen in a oxygenznitrogen mixture which permits the sample to burn; the LOI being calculated as follows:

2] t021+rN21 Thus, a higher LOI is indicative of a higher degree of flame retardancy.

FLAMMABILITY OF POLYPROPYLENE POLYBLENDS Polyblend composition (parts crosslinked copolymer/pts. polypropylene) LOI value 0/ 100 17.6 30/ 100 21.5

30/100+6% of antimony trioxide as based on the weight of the polypropylene 23.8

The above data reveal the improved fire retardancy of the polyblends of this invention as well as the fact that the use of a relatively low concentration of antimony trioxide in combination with the tire retardant crosslinked copolymer additive of this invention affects an additional increase in the fire retardancy displayed by one of the novel polyblend of this invention.

Comparable fire retardant polyblends are obtained upon blending this crosslinked copolymer additive with various burning thermoplastics including polymethyl methacrylate, polystyrene, polyethylene, cellulose acetate, nylon 66, polyphenylene oxide, polycarbonate and polyurethane resins. Moreover, excellent fire retardant polyblends are also provided by the use of the following crosslinked vinyl halide copolymers:

( 1) A :5 vinyl chloridezallyl methacrylate copolymer;

(2) A 45:45:10 vinyl chloride:vinyl bromidezallyl methacrylate copolymer;

(3) A 90:10 vinyl chloridezethylene glycol dimethacrylate copolymer;

(4) A 95:5 vinyl chloridezZ-vinyloxyethyl ether copolymer;

(5) A 90:5:5 vinyl bromidezallyl methacrylate copolymerzvinylidene chloride copolymer;

(6) An 80:20 vinyl chloridezethyl diallylphosphonate c0- polymer.

Example II This example illustrates the preparation of another of the crosslinked vinyl halide copolymer additives of this invention as well as its use in the preparation of a fire retardant polyblend with an ABS resin.

Ninety-five parts of vinyl chloride and five parts of allyl methacrylate are suspension polymerized in a solution of 0.5 part of methyl cellulose in 300 parts of deionized water which also contains 0.5 part of t-butyl peroxypivalate as an initiator. The latter mixture is stirred at 60 C. for 10 hours while in a nitrogen atmosphere. The resulting crosslinked 95:5 vinyl chloride allyl methacrylate copolymer is isolated by filtration followed by washing with water and drying at 70 C. for 24 hours. The copolymer is obtained in a yield of 98% and contains 50%, by weight, of chlorine.

A polyblend containing 70 parts of an ABS resin sold by the Marbon Chemical Division of the Borg-Warner Corp. as Blendex-31l along with 22 parts of the above described cross-linked copolymer and 8 parts of antimony trioxide is prepared by milling a mixture of the latter ingredients for 10 minutes on a two-roll mill in which the front roll is at a temperature of 330 F. and the backroll is at 310 F. As shown in the following table, the resulting blend, as compared with unmodified ABS resin, displays reduced flammability upon having its limiting oxygen index (LOI) determined by means of ASTM D-2863.

FLAMMABILITY OF ABS RESIN POLYBLEND Polyblend composition (parts crosslinked copolymer/parts ABS resin):

/ 100 22/70+8 parts of antimony trioxide and 0.6 part of a tin mercaptide stabilizer sold by M & T Chemicals, Inc. as Thermolite 31 24.4

The above data again illustrate the improved fire retardancy developed in the polyblends containing the novel crosslinked copolymer additives of this invention.

Variations may be made in proportions, procedures and materials without departing from the scope of this invention as defined in the following claims.

What is claimed is:

1. A fire retardant polyblend comprising an intimate admixture of poly(alpha-olefins) and an eifective flame retarding concentration of at least one crosslinked copolymer of: (1) at least one vinyl halide selected from the group consisting of vinyl chloride, vinyl bromide and vinyl fluoride present in a concentration of from 50-99% by weight and (2) at least one polyfunctional ethylenically unsaturated monomer, present in a concentration of from about 1-50%, by weight.

2. The polyblend of claim 1, wherein the polyfunctional ethylenically unsaturated monomer of said crosslinked copolymer is selected from the group consisting of allyl methacrylate, divinyl benzene, ethylene glycol dimethacrylate, trimethylolpropane, trimethacrylate, methylene-bis-acrylamide, diethylene glycol diacrylate, ethylene glycol diacrylate, divinyl ether, diallyl adipate, 2-vinyloxyethyl ether, diallyl fumarate, diallyl phthalate, divinyl sulfone, divinyl carbitol, butylene dimethacrylate, trimethylene glycol diacrylate, butylene glycol diacrylate, pentamethylene glycol diacrylate, glyceryl triacrylate, octylene glycol diacrylate, trimethylene propanetriacrylate, the tetraacrylate ester of pentaerythritol and ethyl diallylphosphonate.

3. The polyblend of claim 2, wherein the polyfunctional ethylenically unsaturated monomer of said crosslinked copolymer is allyl methacrylate.

4. The polyblend of claim 1, wherein the vinyl halide of said crosslinked copolymer is vinyl chloride.

LOI value 17.8

5. The polyblend of claim 1, wherein said crosslinked copolymer also contains up to about 49%, by weight, of at least one optional monofunctional vinyl comonomer.

6. The polyblend of claim 1, wherein said crosslinked vinyl halide copolymer is present in a concentration of from about 5 to 50% of the total weight of said polyblend.

7. The polyblend of claim 1, wherein said poly(alphaolefin) polymer is polypropylene.

8. The polyblend of claim 7, wherein antimony trioxide is also present.

9. A fire retardant polyblend comprising an intimate admixture of poly(alpha-olefins) and an effective flame retarding concentration of a crosslinked copolymer of from about 50-99% by weight, of vinyl chloride and from about 1-50%, by weight of a polyfunctional ethylenically unsaturated monomer.

10. The polyblend of claim 9, wherein the polyfunctional ethylenically unsaturated monomer of said crosslinked copolymer is selected from the group consisting of allyl methacrylate, divinyl benzene, ethylene glycol dimethacrylate, trimethylolpropane, trimethacrylate, methylene-bis-acrylamide, diethylene glycol diacrylate, ethylene glycol diacrylate, divinyl ether, diallyl adipate, 2-vinyloxyethyl ether, diallyl fumarate, diallyl phthalate, divinyl sulfone, divinyl carbitol, butylene dimethacrylate, trimethylene glycol diacrylate, butylene glycol diacrylate, pentamethylene glycol diacrylate glyceryl triacrylate, octylene glycol diacrylate, trimethylene propane triacrylate, the tetraacrylate ester of pentaerythritol and ethyl diallylphosphonate.

11. The polymer composition of claim 10, wherein the polyfunctional ethylenically unsaturated monomer of said crosslinked vinyl chloride copolymer is allyl methacrylate.

12. The polymer composition of claim 9, wherein said crosslinked vinyl chloride copolymer also contains up to about 49%, by weight of at least one optional monofunctional vinyl comonomer.

13. The polyblend of claim 9, wherein said crosslinked vinyl chloride copolymer is present in a concentration of Iigrom about 5 to 50%, of the total weight of said polylend.

14. The polyblend of claim 9, wherein said poly(alphaolefin) polymer is polypropylene.

15. The polyblend of claim 14, wherein antimony trioxide is also present.

References Cited UNITED STATES PATENTS 3,345,434 10/ 1967 Griffith 260-901 3,326,828 6/1967 Melio 26023 FOREIGN PATENTS 1,043,058 9/1966 Great Britain 260l MURRAY TILLMAN, Primary Examiner C. J. SECCURO, Assistant Examiner US. Cl. X.R.

26023 R, 23 XA, 23.7 H, 28.5 A, 17 R, 30.6 R, 31.8 M, 45.7 R, 45.7 P, 46.75 K, 45.75 B, 45.8 N, 859 R, 859 PV, 862, 873, 857 UN, 876, 890, 891, 895, 898, 899, 901, DIG. 24 

